Implantable medical devices for treating irregular contractions of the heart with electrical stimuli are known. Exemplary implantable devices are defibrillators and pacemakers. Various types of electrical leads for defibrillators and pacemakers have been suggested, many of which are placed transvenously. Such leads are introduced into the patient's vasculature at a venous access site and travel through veins to the sites where the leads' electrodes will be implanted or otherwise contact target coronary tissue. Electrodes for transvenously-placed leads can be implanted in the endocardium (the tissue lining the inside of the heart) of the right atrium or ventricle, or alternatively, in the branch vessels of the coronary venous system. In particular, lead electrodes can be implanted in the coronary sinus or a branch vessel thereof for sensing and/or stimulation of the left side of the heart (i.e., the left ventricle).
Various techniques have been used to facilitate fixation of the foregoing types of leads at the desired implantation sites. For leads partially implanted within the coronary venous system, fixation techniques should be substantially atraumatic and yet provide fixation sufficient to withstand natural heart motion and retrograde blood flow which naturally tend to push the lead out of the branch vessel into which the electrode is implanted. Additionally, it is desirable to permit and facilitate partial or complete removal of the lead and fixation structures after implantation if necessary or desired.
Accordingly, there is a continuing need for improved devices and methods for fixation of cardiac leads in the coronary venous systems. In particular, there is a need in the art for a fixation approach that effectively secures the lead electrodes in the target coronary branch vessel while still permitting subsequent removal of the lead.